The Bacillus subtilis response regulator SpoOA stimulates transcription of the spoIIG operon through modification of RNA polymerase promoter complexes

Sporulation in Bacillus subtilis is dependent on the response regulator SpoOA, which both represses and activates transcription in vitro. The activity of SpoOA is increased by phosphorylation. We previously demonstrated that the phosphorylation increased the ability of SpoOA to stimulate in vivo transcription from the promoter for the spoIIG operon, one of the operons known to be regulated by SpoOA in vivo. In the work reported here we have examined the kinetics of transcription initiation at the spoIIG operon promoter using a single round transcription assay and the kinetics of formation of spoIIG promoter-RNA polymerase complexes using DNase I footprinting. Both the kinetic assays and the footprint assays indicated that the initial binding of the polymerase to the template was not dependent on the presence of SpoOA. The phosphorylated form of SpoOA stimulated the rate of initiation by affecting a step that occurred after the initial interaction of the polymerase with the template. Phosphorylation of SpoOA may stimulate transcription by modifying preinitiation complexes containing the polymerase and the promoter. (C) 1996 Academic Press Limited